Transcriptomic differences noted in Glaesserella parasuis between growth in broth and on agar

Potential role of key rumen microbes in regulating host health and growth performance in Hu sheep

BACKGROUND

Average daily gain (ADG) is an important component affecting the profitability of sheep. However, research on the relationship between rumen microbes and sheep growth phenotype is still very lacking. Therefore, in this study, 16 Hu sheep were selected from a cohort of 318 sheep assigned to the same feeding and management conditions, and divided into high growth rate (HADG, n = 8) group and low growth rate (LADG, n = 8) group according to the extreme ADG value. Then, the differences in rumen microbes, rumen fermentation and animal immune parameters were further compared between groups to explore the potential role of rumen key microbes in regulating the health and growth performance of Hu sheep hosts.

RESULTS

The results showed that specific pathogenic bacteria associated with ADG, including Anaerotruncus, Sediminibacterium and Glaesserella, exhibited significant correlations with interleukin-6 (IL-6) and immunoglobulin G (IgG). These interactions disrupt immune homeostasis in the host, leading to a metabolic prioritization of energy resources toward immune responses, thereby impairing growth and development. Succinivibrio_dextrinosolvens was enriched in HADG sheep and exhibited a significant positive correlation with propionate levels. This promoted propionate production in the rumen, enhancing the metabolic activity of carbohydrate, amino acid and energy metabolism, ultimately contributing to higher ADG in sheep. Importantly, random forest analysis results showed that Succinivibrio_dextrinosolvens could classify sheep into HADG and LADG with a prediction accuracy of 81.2%. Additionally, we identified 34 bacteria belonged to connectors in the HADG co-occurrence network, including Alloprevotella, Phascolarctobacterium, Anaerovibrio, Butyricicoccus, Ruminococcaceae_noname, and Roseburia, etc., which play an important role in the degradation of carbohydrates and convert them into short-chain fatty acids (SCFAs), maintaining rumen health, and modulating inflammation.

CONCLUSIONS

In summary, key microbes in the rumen affect the overall healthy homeostasis and rumen fermentation of the host, leading to changes in energy utilization, which in turn affects the average daily gain of Hu sheep. Succinivibrio_dextrinosolvens is a promising biomarker for selecting high growth rate sheep in the future. This study provides a new method to manipulate rumen bacteria to improve growth performance in sheep.

Transcriptional profile of Glaesserella parasuis in swine serosal and joint fluids

Glaesserella parasuis is the causative agent of Glässer's disease and contributes to significant post-weaning mortality in the swine industry. Glässer's disease is characterized by meningitis, polyserositis, and polyarthritis. Previous work has examined transcriptomic differences of G. parasuis when inoculated into different in vitro conditions, lung explants, or the lung in vivo following intratracheal challenge. However, it is still unknown how the transcriptome of G. parasuis may change to cause polyserositis or polyarthritis. Here, we incubated G. parasuis in acellular joint or serosal fluid for 3 and 12 hours to better understand transcriptional changes in the joint or serosal compartment. When G. parasuis serovar 5 strain 29755 was incubated in host fluid for 3h, cell wall, membrane, and envelope biogenesis genes were downregulated compared to G. parasuis incubated in PBS. In contrast, translation, ribosomal structure, and biogenesis and carbohydrate transport and metabolism were upregulated in the host fluid compared to PBS. Additionally, there were eleven differentially expressed genes with an unknown function shared between the acellular joint and serosal fluid at the 3h timepoint compared to PBS. When comparing the differences between the host fluids from 12 to 3h and the host fluids at 3h compared to PBS, this study found sixteen genes with inverse expression patterns. An investigation into the hypothetical genes identified and the nineteen shared genes in all comparisons may provide further knowledge about the pathogenesis of G. parasuis, which may be useful in developing interventions against Glässer's disease.

Novel type II toxin-antitoxin systems with VapD-like proteins

Type II toxin-antitoxin (TA) systems are widespread in prokaryotes. They consist of neighboring genes encoding two small proteins: a toxin that inhibits a critical cellular process and an antitoxin that binds to and neutralizes the toxin. The VapD nuclease and the VapX antitoxin comprise a type II TA system that contributes to the virulence of the human pathogen Haemophilus influenzae. We analyzed the diversity and evolution of VapD-like proteins. By examining loci adjacent to genes coding for VapD-like proteins, we identified two novel families of antitoxins, which we named VapY and VapW. VapD toxins cognate to novel antitoxins induce the SOS response when overproduced, suggesting they target cellular processes related to genomic DNA integrity, maintenance, or replication. Though VapY has no sequence similarity to VapX, they share the same SH3 fold characterized by the five anti-parallel β sheets that form a barrel. VapW is a homolog of VapD without conserved catalytic residues required for nuclease activity. The crystal structure of the VapD-VapW complex reveals that VapW lacks the dimerization interface essential for the catalytic activity of VapD but retains the second interaction interface that enables VapD hexamerization. This allows VapW to bind VapD in the same manner that VapD dimers bind to each other in hexamers. Thus, though the VapD catalytic cleft remains accessible in the VapD-VapW complex, VapW may disrupt VapD oligomerization. To our knowledge, VapWD provides a unique example of TA systems evolution when a toxin loses its activity and becomes an antitoxin to itself.

IMPORTANCE

Genes encoding virulence-associated protein D (VapD) homologs are found in many pathogens such as Helicobacter pylori, Haemophilus influenzae, and Xylella fastidiosa. There are many indications that VapD proteins contribute to virulence, even though the exact mechanism is not known. VapD proteins are either encoded by stand-alone genes or form toxin-antitoxin pairs with VapX. We performed a comprehensive census of vapD-like genes and found two new antitoxins, VapW and VapY. The VapW antitoxins are catalytically inactivated variants of VapD, revealing a new evolutionary mechanism for the appearance of toxin-antitoxin pairs.

The Role of Antibodies Against the Crude Capsular Extract in the Immune Response of Porcine Alveolar Macrophages to In Vitro Infection of Various Serovars of Glaesserella (Haemophilus) parasuis

In Glässer’s disease outbreaks, Glaesserella (Haemophilus) parasuis has to overcome the non-specific immune system in the lower respiratory tract, the alveolar macrophages. Here we showed that porcine alveolar macrophages (PAMs) were able to recognize and phagocyte G. parasuis with strain-to-strain variability despite the presence of the capsule in virulent (serovar 1, 5, 12) as well in avirulent strains (serovar 6 and 9). The capsule, outer membrane proteins, virulence-associated autotransporters, cytolethal distending toxins and many other proteins have been identified as virulence factors of this bacterium. Therefore, we immunized pigs with the crude capsular extract (cCE) from the virulent G. parasuis CAPM 6475 strain (serovar 5) and evaluated the role of the anti-cCE/post-vaccinal IgG in the immune response of PAMs to in vitro infection with various G. parasuis strains. We demonstrated the specific binding of the antibodies to the cCE by Western-blotting assay and immunoprecipitation as well as the specific binding to the strain CAPM 6475 in transmission electron microscopy. In the cCE, we identified several virulence-associated proteins that were immunoreactive with IgG isolated from sera of immunized pigs. Opsonization of G. parasuis strains by post-vaccinal IgG led to enhanced phagocytosis of G. parasuis by PAMs at the first two hours of infection. Moreover, opsonization increased the oxidative burst and expression/production of both pro- and anti-inflammatory cytokines. The neutralizing effects of these antibodies on the antioxidant mechanisms of G. parasuis may lead to attenuation of its virulence and pathogenicity in vivo. Together with opsonization of bacteria by these antibodies, the host may eliminate G. parasuis in the infection site more efficiently. Based on these results, the crude capsular extract is a vaccine candidate with immunogenic properties.

Expression of virulence factors under different environmental conditions in Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a facultative anaerobic Gram-negative bacterium associated with periodontal diseases, especially aggressive periodontitis. The virulence factors of this pathogen, including adhesins, exotoxins, and endotoxin, have been extensively studied. However, little is known about their gene expression mode in the host. Herein, we investigated whether culture conditions reflecting in vivo environments, including serum and saliva, alter expression levels of virulence genes in the strain HK1651, a JP2 clone. Under aerobic conditions, addition of calf serum (CS) into a general medium induced high expression of two outer membrane proteins (omp100 and omp64). The high expression of omp100 and omp64 was also induced by an iron-limited medium. RNA-seq analysis showed that the gene expressions of several factors involved in iron acquisition were increased in the CS-containing medium. When HK1651 was grown on agar plates, genes encoding many virulence factors, including the Omps, cytolethal distending toxin, and leukotoxin, were differentially expressed. Then, we investigated their expression in five other A. actinomycetemcomitans strains grown in general and CS-containing media. The expression pattern of virulence factors varied among strains. Compared with the other five strains, HK1561 showed high expression of omp29 regardless of the CS addition, while the gene expression of leukotoxin in HK1651 was higher only in the medium without CS. HK1651 showed reduced biofilm in both CS- and saliva-containing media. Coaggregation with Fusobacterium nucleatum was remarkably enhanced using HK1651 grown in the CS-containing medium. Our results indicate that the expression of virulence factors is altered by adaptation to different conditions during infection.